This invention relates to a nuclear magnetic resonance apparatus for measuring the concentration distribution of a specific atomic nucleus in a body to be examined and/or the relaxation time of the same from the outside of the body by making use of the nuclear magnetic resonance (NMR) phenomena.
The construction adjacent the magnetic field generating part of a recently developed examining NMR apparatus is shown in FIG. 1. (See application filed concurrently herewith under the title "Nuclear Magnetic Resonance Apparatus Utilizing Multiple Magnetic Fields".) As shown, a homogeneous static magnetic field is generated by a pair of electromagnets 1 in the space between their pole plates 2. The direction of that magnetic field is designated by the arrow Z. Also, a gradient magnetic field is superimposed in the direction Z by a pair of electromagnets 3. The resulting magnetic fields are shown in FIG. 2.
In FIG. 2, the axis of abscissas designates the position of the magnetic field in the direction Z and the axis of ordinates designates the intensity of the magnetic field at each position. Although the intensity of the magnetic field is constant regardless of its position in the direction Z if there is only the homogeneous magnetic field, as shown by a broken line H1, the total field changes in accordance with the positions in the direction Z if the gradient magnetic field shown by a phantom line H2 is added to the homogeneous magnetic field, as shown by the solid line H3, so that a gradient intensity distribution of the total magnetic field may be obtained in the direction Z.
For example, when measurements are performed by using a phantom (or a model of a body to be examined) 4, a part 4a of which has a preassigned low concentration of hydrogen nuclei, for example, the intensity of a nuclear magnetic resonance signal is obtained with the result shown in FIG. 3(a), having a deflection 4a, in the intensity of the magnetic field. Since the intensity of the magnetic field, as shown by the resonance signals, and the position of the field in the direction Z are in a corresponding relation, as shown in FIGS. 1, 2 and 3, the intensity of the NMR signal obtained represents the projection datum in the direction perpendicular to the direction Z in the particular section of the phantom. Therefore, if projection data in each direction are obtained, the concentration distribution image of a specific atomic nucleus (for example, hydrogen nucleus) in the section can be reconstructed in the same manner as in the case of computed tomography (CT).
For realizing this result, the apparatus of FIG. 1 has been able to obtain such data only while rotating the body, such as the phantom 4, within the magnet frame. For example, the signal shown in FIG. 3 (b) is obtained when the phantom 4 has been rotated 90 degrees. In FIG. 1, a coil 5 wound around the phantom 4 is used for detecting the nuclear magnetic resonance signal after adding a high-frequency electromagnetic pulse train to the body.
As described above, since the examining NMR apparatus in FIG. 1 applies a gradient magnetic field in only one direction, the following means have been needed for obtaining projection data as to a section of the body:
(a) to obtain the signal while rotating the body within the magnetic frame; or
(b) to obtain the signal while rotating the magnet frame around the body.
A rotating scan apparatus is obviously needed for obtaining the result by either means. In either case, the scan is time-consuming. Additionally, it is feared that the rotation of the body may involve movement of portions of the body, or interaction of parts of the body, which may be damaging to an already unhealthy body. The magnet frame involves considerable weight, and the rotation of the frame is burdensome and difficult.